U.K. Patent Application No. 2,075,023 teaches the use of 5-30 phr of castor oil in SBR or polybutadiene latex foam rubber to impart resistance to charring. U.K. Patent Application No. 2,076,404 teaches the use of thiols, disulphides, aliphatic primary amines, guanidines or guanidine derivatives in a polybutadine or SBR latex foam rubber containing up to 40 percent by weight of natural rubber latex in order to produce a non-smoldering foam.
There are several well known additives for imparting flame retardance to a foam material. Inorganic flame retardants such as antimony oxide may be added to the foam composition. Halogen generating compounds such as chlorinated paraffin wax may be added to the foam composition. The foam composition may be modified by the addition of a phosphate flame retardant. It is also known that the above additives may be used in combination.
While a flame retardant will supress the propagation of open flame, it may not be useful to prevent internal charring and applicant has found that most of the conventional flame retardant additives do not prevent internal charring of styrene-butadiene latex foam rubber. Applicant has found that certain organic phosphates, butyl benzyl phthalate or mixtures of these do give substantially improved resistance to internal charring.